LOCTITE SI 5660 A 1-part, gray, flexible, non-corrosive flange sealant for applications involving large gaps. LOCTITE SI 5660 is a silicone sealant and cures on exposure to moisture in the air to form a tough rubber gasket. The nature of LOCTITE SI 5660 reduces the migration of liquid product after application to the part. It has been designed especially for gasketing applications where good resistance against oils and coolants is required. Typical applications include transmissions and cast metal housings.